Our previous study demonstrated that the application of ultrasound to the rat cremaster muscle produces effects consistent with the hypothesis that ultrasound can increase tissue oxygen tension. The objectives of this study are: 1) to test the hypothesis that ultrasound increases oxygen tension in normal resting skeletal muscle; 2) to measure the change in oxygen extraction and tissue oxygen concentration produced by insonating ischemic tissue (skeletal muscle); 3) to investigate the hemodynamic effects of ultrasound on the arterioles and venules, as well as tissue oxygen tension in skin and connective tissue (bat wing model; and 4) to determine whether therapeutic levels of ultrasound produce any effects upon lymphatic cynamics. Tissue oxygen tension and consumption will be evaluated with the Whalen PO2 microelectrode. Hemodynamic status of the microvasculature will be assessed by microscopic measurement of arteriolar and venular lumen diameter, and red blood cell velocity. Lymphatic activity will be quantified by measuring intraluminal pressure with a Wiederhielm micropressure servosystem. One MHz ultrasound at intensities in the range 1.0 - 10.0 W/cm squared (temporal average, spatial peak) will be applied to both muscle and skin. A pulsed format will be utilized to avoid standing wave formation (5KHz P.R.F.). All protocols include thermal control experiments in an attempt to separate thermal and mechanical effects of the sound. This study combines the techniques of microvascular physiology with the discipline of biophysical acoustics to investigate several problems of possible clinical significance. The experiments in muscle will determine whether ultrasound can increase tissue oxygenation. If this proves tru, it may be possible to design more efficient mechanisms for treating ulcerations, and other impaired tissues, with ultrasound. The study in skin will establish whether any beneficial or adverse effects can be attributed to ultrasound in the organ most easily accessible to sound. The potential for increasing lymphatic pumping ability, and thereby aiding the reduction of tissue edema, is the rationale for the studies on lymphatics in the bat wing.